Many children and adolescents with mental disorders in the United States are treated with multiple psychotropic medications even though there is not much information on how well these medications work together or if they are safe to administer together. Many youth with ADHD have co-occurring (comorbid) disorders such as oppositional-defiant disorder, anxiety disorders, and mood disorders. There is much interest in the treatment of children and adolescents with comorbid ADHD and anxiety disorders because this is a common condition in clinical practice. When children with both anxiety and ADHD receive stimulant medication for ADHD, their anxiety may not improve. SSRI medications represent a reasonable addition to stimulant treatment, as they are considered effective for anxiety disorders based on controlled trials in adults and open trials in children. However, there are no data from controlled studies regarding the tolerability and dosing of the combination of stimulant treatment (including methylphenidate) and SSRIs in the treatment of children with comorbid ADHD and anxiety disorder.